Download readline from http://ftp.gnu.org/pub/gnu/readline/readline-4.3.tar.gz into /usr/local/src

Extract readline in /usr/local/src, configure, compile, and install:

su - root
cd /usr/local/src
tar xvfz readline-4.3.tar.gz
readline-4.3
./configure
make
make install

Proceed with the Unix-like system instructions. OS X is incompatible with Oracle 8, and Oracle 9i on OSX is not yet verified for OpenACS. So continue with Install PostgreSQL. Additional special steps for OS X are documented inline with the standard Unix-like instructions.